Answer:
(i) since otherwise resources are idle.
(ii) since it would be impossible to produce more of one thing without producing less of another.
Explanation:
When an economy has reached productive efficiency, all resources are being fully utilized such that if the country wants to produce more of one good, they would have to produce less of another.
It is important that a country achieves this level because it would mean that no resource is being left idle and there is no under-performance in the economy.
